1. Field of the Invention
The present invention relates to techniques used in the field of microbial industry. More precisely, the present invention relates to a method for producing L-lysine or L-arginine by fermentation and a microorganism used in the production method.
2. Brief Description of the Background Art
Amino acids such as L-lysine, L-glutamic acid, L-threonine, L-leucine, L-isoleucine, L-valine and L-phenylalanine are industrially produced by fermentation using microorganisms such as those that belong to the genus Brevibacterium, Corynebacterium, Bacillus, Escherichia, Streptomyces, Pseudomonas, Arthrobacter, Serratia, Penicillium, Candida, or the like. In order to improve the productivity of these microorganisms, strains isolated from nature or artificial mutants thereof have been used. Moreover, various techniques have been disclosed for increasing the L-amino acid producing abilities by using recombinant DNA techniques to enhance L-amino acid biosynthetic enzymes.
Production of L-amino acids has been improved considerably by breeding microorganisms such as those mentioned above, and improving various production methods. However, in order to respond to further increase in demand in the future, development of methods for more efficient production of L-amino acids at a lower cost are still desirable.
Methods for producing L-amino acids by fermentation of methanol, which is a fermentation raw material available in large amounts at a low cost, include known methods using microorganisms that belong to the genus Achromobacter or Pseudomonas (Japanese Patent Laid-open (Kokai) No. 45-25273), Protaminobacter (Japanese Patent Publication (Kokoku) No. 49-125590), Protaminobacter or Methanomonas (Japanese Patent Laid-open No. 50-25790), Microcyclus (Japanese Patent Laid-open No. 52-18886), Methylobacillus (Japanese Patent Laid-open No. 4-91793), Bacillus (Japanese Patent Laid-open No. 3-505284) and so forth. The inventors of the present invention have developed methods for producing L-amino acids using Methylophilus bacteria based on breeding by artificial mutagenesis and recombinant DNA techniques (Japanese Patent Application No. 11-368097).
In recent years, proteins have been identified that specifically secrete an L-amino acid to the outside of a cell, as well as the genes therefor. In particular, Vrljic et al. identified a gene which is involved in the secretion of L-lysine from a Corynebacterium bacterium to outside of a cell (Vrljic M., Sahm H., Eggeling L., Molecular Microbiology 22:815-826 (1996)). This gene was designated lysE, and it was reported that the L-lysine producing ability of Corynebacterium bacteria could be improved by enhancing this gene in Corynebacterium bacteria (WO97/23597). It is also known that production of some L-amino acids can be improved by increasing the expression of amino acid excreting proteins in Escherichia coli (Japanese Patent Laid-open No. 2000-189180). For example, it has been reported that production of cysteine, cysteine, and so forth can be improved by enhancing expression of ORF306 gene in Escherichia coli (EP885962).
However, there has been disclosed no indication that the amino acid excretion process constitutes a serious obstacle for amino acid production by fermentation of methanol in methanol assimilating bacteria. Furthermore, there have been no reports as to any amino acid excretion gene that can provide such a secretion activity in a methanol assimilating bacterium.
Furthermore, it has not been previously reported that the lysE gene has a function of excreting amino acids other than L-lysine.